Binge eating is thought to involve significant alterations in brain serotonin levels and receptors that may serve to sustain overeat/restrict patterns of behavior. These changes may also contribute to associated comorbitidy such as depression, alcoholism and obesity. The neurochemical causes and consequences of repeated episodes of binge-type behavior, however, have been difficult to examine directly using human subjects. Furthermore, few animal models have been developed for use in this type of research. The purpose of the proposed research is to examine changes in serotonin levels, receptor density, and sensitivity to serotonergic agonist using a novel rat "binge-eating" procedure developed in my laboratory. In this procedure, nonfood deprived rats are allowed to "nibble" or "binge" on an optional source of fat or carbohydrate for four weeks. After the four-week period, discrete brain regions will be assayed before, during, and after a carbohydrate or fat "binge" and behavioral responses to selective serotonergic agonists will be determined. Three experiments will determine the affects of binge-type behavior on (1) levels of serotonin in discrete brain nuclei, (2) 5HT1B receptor density in discrete brain nuclei, (3) sensitivity to 5HT1B and 5HT2C receptor agonists. The independent contributions of consumption pattern and type of food consumed to changes in serotonin and its receptors will be systematically evaluated. These studies will provide important basic information relevant to understanding the neurobiological consequences of binge-type eating behavior.